US7428360B2 - Optical waveguide sensor and method of manufacture - Google Patents
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- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
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- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
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Abstract
An optical waveguide environmental sensor is provided that is capable of detecting a target gas or liquid in the ambient environment in an advantageously short period of time. The waveguide is preferably in the form of an optical fiber having a cladding that contains a photonic band gap structure which in turn envelopes a light conducting, hollow core portion. The cladding further includes at least one elongated side opening that preferably extends the entire length of the fiber and exposes said hollow core portion to the ambient environment, which provides broad and nearly immediate access of the core portion to gases and liquids in the ambient environment, thereby minimizing sensor response time. The ambient gases or liquids filling the hollow core portion and elongated opening function as a ridge and slab, respectively, of an optical ridge waveguide that effectively supports at least one bound optical mode.
Description
This is a divisional application of U.S. application Ser. No. 11/711,199, filed Feb. 27, 2007, now U.S. Pat. No. 7,343,074 entitled “Optical Waveguide Environmental Sensor and Method of Manufacture”.
This invention generally relates to an optical waveguide environmental sensor and the method of manufacturing the same, and is specifically concerned with such a sensor in the form of a photonic band gap fiber having an elongated side opening that exposes its hollow core to the ambient environment.
Environmental sensors in the form of optical fibers having a hollow core are known in the prior art. The hollow core of the fibers used for such sensors typically conducts light by way of a photonic band gap structure (PBG) surrounding the hollow core having a “forbidden frequency range” which corresponds to the wavelength of the light transmitted through the fiber, although hollow core fibers that conduct light via total internal reflection (TIR) for a specific range of wavelengths are also known. Such sensors may be used to sense the presence of a particular gas or liquid in the ambient environment, for example a threshold amount of carbon dioxide in the ambient air which may be indicative of a fire or other unsafe condition. In one prior art design, the hollow core of the optical fiber is exposed to the ambient atmosphere at one or both of the ends of the fiber to allow gases from the ambient atmosphere to continuously flow into a hollow core of the fiber. In operation, laser light having a wavelength which would be absorbed by the particular gas composition to be a detected is continuously conducted through the hollow core of the fiber. When such a gas is introduced into the open end of the fiber from the ambient atmosphere, it begins to flow through the hollow core, and the amplitude of the laser light transmitted through the core diminishes due to absorption of the light by the gas. In the case light transmitted through the core diminishes due to absorption of the light by the gas. In the case of the carbon dioxide example referred to earlier, the diminishment of the amplitude of the light below a certain threshold may be used to generate a signal that triggers a fire alarm circuit.
Such environmental sensors may be used to detect a broad variety of different gas compositions in the atmosphere, organic and inorganic particulates or vapor droplets, and even different liquid compositions when the fiber is immersed in a liquid. Hence such sensors have a broad applicability as detectors of not only combustion products or polluting or potentially toxic substances, but also as control or monitoring sensors in industrial manufacturing processes where the control of the composition of a particular gas or liquid is required.
Unfortunately, there are a number of shortcomings associated with such prior art optical fiber environmental sensors. As previously pointed out, access to the ambient environment is provided only at one or both of the ends of the fiber, where the relatively tiny diameter of the hollow portion is exposed to the outside atmosphere. Such restricted access to the hollow core of the sensor fiber results in a relatively long response time for such a sensor to detect a particular “target” gas or liquid. For example, for a known optical fiber sensor having a length of 21 cm, a response time of 2 minutes is required from the time that the target gas or liquid is first introduced into the hollow core of the fiber before the fiber sensor generates a signal indicating that the target gas or liquid is present. Such a long response time substantially limits the usefulness of such sensors in many applications, such as chemical manufacturing applications, where a 2 minute delay may result in the irretrievable ruin of a production run of an expensive composition.
Thus far, no satisfactory way to shorten the response time for such sensors has been found. Of course, the length of the optical fiber sensor could be shortened, but such shortening not only reduces the sensitivity of the sensor (as sensitivity is proportional to the total volume of the hollow core) but also makes it apt to generate false positives (as a single tendril of cigarette smoke curling around a 1 cm smoke detector may trigger it).
Another solution to shorten the response time might be to make the diameter of the fiber air core larger. Such a solution might be implemented by using capillary tubes with hollow cores having a diameter on the order of 1.0 mm that conduct light via grazing incidence scattering rather than by the use of TIR or a PBG. However, such capillary tube optical waveguides have high light losses of over 1 dB/m, which imposes practical limits on the length of such a sensor, and are also relatively stiff and inflexible, which prevents them from being installed in space-limited situations where a sharp bending or tight coiling of the sensor is desired. To reduce the losses associated with such a capillary tube design, the hollow interior of the tube might be coated with alternating layers of materials having sharply different indexes of refraction, thereby creating a Bragg reflector, or a single layer of a material having an index of refraction less than air. However, such coated capillary tubes would be substantially more expensive to manufacture than drawn optical fibers. Additionally, the losses would still be greater than 0.5 dB/m, and the problems associated with stiffness and inflexibility would remain. In addition, many optical sensing operations rely on nonlinear optical effects (Raman spectroscopy, for example) for which the sensitivity is proportional to the intensity (power per area) of the optical signal. A larger optical core will cause the intensity of the light in the core to decrease by a factor proportional to the square of the diameter of the core thereby reducing the device sensitivity by the same factor.
Finally, it has been proposed to laser drill a plurality of circular side holes in the fiber to better expose the hollow core to the ambient atmosphere. While such a solution may shorten the response time of the fiber sensor, the resulting response time would still be unacceptably long due the fact that access to the hollow core is still quite limited. Additionally, there is a concern in the prior art that such radially-oriented side openings create “light leaks” that limit the number of side openings that can be fabricated in such a fiber before the resulting losses become unacceptably high.
Clearly, what is needed is an optical waveguide environmental sensor that maintains the low losses, flexibility and ease of manufacture associated with optical fibers, but which substantially reduces the response time associated with fiber-based environmental sensors that rely upon a relatively small number of end or side holes to expose the hollow core of the fiber to the ambient environment.
Generally speaking, the invention is an optical waveguide environmental sensor that overcomes the aforementioned shortcomings associated with prior art. To this end, the environmental sensor of the invention comprises a cladding having a hollow core portion that extends along or parallel to a longitudinal, center axis of the cladding and defines a light transmission path through the waveguide, and at least one elongated side opening in the cladding that extends parallel to the longitudinal center axis and directly exposes all or a substantial part of the side of the hollow core portion to the ambient environment, wherein the hollow core portion and the elongated opening support at least one bound optical mode. The optical wave-guide is preferably an optical fiber that includes a photonic band gap structure which envelops the hollow core portion. The photonic band gap structure may assume the form of either a Bragg reflector that includes alternate layers of material having sharply different indexes of refraction, or a microstructured material having a periodic variation in an index of refraction. In operation, when a gas or liquid from the ambient environment fills the hollow core portion and the elongated opening in the cladding, the hollow core portion and elongated opening form a ridge and a slab, respectively, of an optical ridge waveguide sensor that binds an optical mode to the hollow core portion.
The elongated opening preferably runs most or all of the length of the waveguide in order to maximize exposure of the side of the hollow core portion to the ambient environment and to minimize the response time of detection, preferably to seconds or less. The optical waveguide may have a plurality of such elongated openings, each of which operates to expose a side of the hollow core portion to the ambient environment and to further reduce response time. To eliminate optical birefringence, the plurality of elongated openings may be symmetrically disposed around the cladding.
The elongated opening may take the form of a slot-like groove having parallel side walls. Such a slot-like opening may extend through only through one side of the cladding to the hollow core portion, or completely through the cladding thereby exposing two sides of the hollow core portion. Alternatively, the elongated opening may be formed by the removal of a wedge-shaped section of cladding such that the side walls of the opening are disposed at an angle to one another when the waveguide is viewed in cross section. Finally, the elongated opening may also be formed by the removal of a flat-sided section of cladding such that the side walls of the elongated opening are co-planar, thus giving the optical fiber sensor a “D” shaped profile when viewed in cross section. When the elongated opening is formed in this last-described manner, the optical fiber is preferably bent around a radius in a spiral configuration with the flat side of the “D” shaped profile on the inside of the bend in order to reduce light losses in the resulting fiber, as the optical mode conducted through the resulting ridge waveguide is more weakly bound by such an open configuration of the hollow core portion.
The optical fiber sensor of the invention may also have multiple hollow cores which are preferably optically coupled to one another. For example, in such embodiment, one or all of the hollow core portions may be exposed to the ambient environment by one or more elongated openings. For example, in such a sensor one hole may be isolated from the environment to act as a reference optical path, while the other core or cores may be exposed to the environment, there-by producing an interferometric sensor in which light in the reference optical path will interfere with light in the sensing optical path yielding a signal that is related to the concentration of the target gas or liquid species. Such a differential or interferometric sensor according to some embodiments of the present invention can remove the effect of other environmental changes such as temperature and pressure.
Finally, the invention also encompasses a method of fabricating an optical waveguide environmental sensor that comprises the steps of forming an elongated optical waveguide from a light conducting material that contains a hollow core portion surrounded by photonic band gap structure, and forming an elongated opening in a side of said waveguide that is parallel to a longitudinal axis of said waveguide that exposes said hollow core portion to the ambient environment. Preferably, the step of forming said elongated optical waveguide is implemented by the drawing of an air-core photonic band-gap fiber from a light conducting material, while the step of forming the elongated opening is implemented by chemically etching said opening in a side wall of said fiber. When such chemical etching is used to form the elongated opening, a glass composition may be provided in a side of said optical fiber that has a higher etch rate to facilitate the step of chemically etching said opening in a side wall of said fiber. Alternatively, the elongated opening may be formed by laser machining (for example, drilling) said opening in a side wall of said optical fiber. The term “laser machining” as used herein, includes but is not limited to various forms of laser assisted material removal, material redistribution and material modification.
With reference now to FIG. 1 , wherein like numerals designate like components throughout all the several figures, the optical waveguide sensor 1 of the invention preferably comprises a photonic band gap fiber 3 having a lattice-type microstructure 7 hereinafter referred to as cladding 7. The cladding 7 includes a pattern of different light conducting materials having different indexes of refraction, such as a pattern of air holes 8 (shown in FIGS. 2A-4F ) in the silica present in the center of the fiber 3. Alternatively, the cladding 7 may be formed from an alternating pattern of two different solid light conducting materials, such as two different types of glasses, or a glass and a plastic material. Finally, the cladding 7 may be formed from alternating layers of such materials, so long as the differences in the index of refraction between the two materials effectively creates a “forbidden zone” that confines a least one optical mode within the hollow core 5. The cladding 7 is in turn surrounded by a jacket 9. The jacket 9 includes an elongated side opening 11, which, in this example, is a slot 13 that extends substantially the length of the fiber 3. The slot 13 is radially oriented with respect to the circular cross-section of the fiber 3 and exposes a hollow core 5 to the ambient environment, which in this example is the ambient atmosphere. Together the core 5 and slot 13 form a waveguide that guides optical modes that are supported by the joint optical structure. The core 5 is a local enlargement of the slot 13 such that at least one optical mode is supported with a significant fraction of its energy localized to the enlarged region. The mode would have greater than 50%, most preferably more than 75% of its energy in the enlarged region. In operation, ambient gas 15 is allowed to continuously flow through the slot 13 and into the hollow core 5 of the fiber. A source 17 of light (for example, laser light) is optically coupled to one end of the fiber 3 and projects a beam 19 through the hollow core 5. The light source 17 may include a quasi-monochromatic laser source, multiple laser sources (co-propagating or counter-propagating), a broadband light source (such as a tungsten halogen lamp, glow bar, spectral lamp, etc), light-emitting diodes or any other source that is used in sensing applications. The hollow core 5 and the radially oriented slot 13 jointly support at least one optical mode, and more specifically function as the ridge and slab, respectively, of an optical ridge waveguide that supports the propagation of at least one optical mode with more than half of its optical power confined to the region defined by the hollow core 5 and the portion of the radially oriented slot 13 that is directly adjacent to the hollow core 5. The slab in this case does not end at the outer surface of the jacket 9 with the end of the elongated side opening 11, but continues into the ambient atmosphere, thereby forming a “semi-infinite” slab. The center frequency of the beam 19 of light (for example, laser light) is selected so as to be absorbable or modified by a target gas, liquid or particulate substance within the ambient air 15. For example, if the optical waveguide sensor is being used as a fire detector, the central frequency of the beam 19 of light may be selected so as to be absorbed by carbon dioxide. A light sensor 21, which may be a phototransistor, receives the beam 19 of laser light exiting the opposite end of the photonic band gap fiber 3, and generates an electric signal having an amplitude that is dependent upon the amplitude of the beam 19 exiting the end of the photonic band gap fiber 3. The light sensor 21 is in turn connected to a digital processor circuit 23, which continuously monitors the amplitude of the electrical signal generated by the light sensor 21. The processor circuit 23 is programmed such that when the amplitude of the signal received by the light sensor 21 falls below a selected threshold, an alarm circuit (not shown) is triggered.
Alternatively, more elaborate detection methods may be utilized to enhance sensitivity, selectivity, or to add functionality to the sensor. Such schemes may include but are not limited to differential detection (including multiple wavelengths or multiple optical paths), nonlinear spectroscopy (including Raman, coherent anti-Stokes Raman scattering, Brillouin scattering) interferometric detection, polarization-based detection, modal detection, distributed sensing (using nonlinear effects, scattering or optical time domain reflectometry), multi-wavelength detection or a combination of these.
Because the elongated side opening 11 in the photonic band gap fiber 3 provides near immediate access of ambient gases 15 to the hollow core 5 of the fiber 3, the response time of the optical waveguide sensor 1 is nearly immediate. Also, because of the relatively low losses associated with the optical ridge waveguide formed by the hollow core 5 and slot 13, the fiber 3 may be on the order of 10 meters or more long, which in turn results in a high sensitivity and allows the fiber 3 to broadly sample the ambient gases present in a particular area, thereby reducing the chances of false positives and thereby enhancing the over all reliability of the sensor 1.
In FIG. 2G , the photonic band gap fiber 3 has an axis along its length and has a transverse cross-section perpendicular to this axis. The slot 13 has a first axis co-linear to the fiber axis and has a second axis, or transverse axis, that lies perpendicular to the first, extending from the core 5 to the elongated side opening 11. In the presence of a lattice, the slot 13 may have a varying width 12 w(r) perpendicular its radial dimension r. Such is the case in FIGS. 2A-2G because of the air holes 8 in the lattice. The width 12 of the slot is given by the minimum transverse width as measured perpendicular to the radial dimension referred to as the transverse axis. The location of the local width minima may be determined by computing a derivative of the slot width as a function of radial dimension such that dw(r)/dr=0 and the second derivative of the width with respect to r is positive. The core 5 (whose centroid is considered r=0) is given by the void in the periodic lattice that would exist in the absence of the slot 13. Because the core 5 and the slot 13 overlap at least partially, we define the core 5 to extend to include the overlap region to where the slot 13 has its first width minima 14, (as counted from r=0). In the case of multiple slots such as slot 28 a and slot 28 b in FIG. 2C , the core 5 extends to the first width minima along each slot. The hollow core 5 will in general have an irregular shape that may be characterized by a minimum transverse dimension D, a centroid location, an enclosed transverse area A and a perimeter p.
In the fiber sensor 3 illustrated in FIG. 2A , the cladding 7 is formed by a lattice of air holes 8. The lattice structure and materials are chosen such that cladding 7 has a photonic band gap over the targeted wavelength range. The scale of the structure is given a pitch A that is defined as the spacing between unit cells of the periodic structure. In FIG. 2A that pitch would be given by the spacing between the centers of adjacent air holes. The wavelength range of the photonic band gap can be shifted by changing the pitch A, the refractive index n, the type of lattice, and the design of the unit cell of the lattice (including shape). The fiber sensor 3 can be designed for operation across the optical spectrum from the ultraviolet (100-400 nanometers) to the far infrared (20 microns). Although a single glass will not cover such a broad wavelength range without absorption, there are glasses with low optical absorptions in each portion of the spectrum. Examples of these glasses are fused silica, silicates, borosilicates, phosphates, germanates, chalcogenides, ionic glasses (such as halides, nitrates, sulfates and carbonates), and glass ceramics. Additionally optical polymers including acrylates such as PMMA and perfluorinated polymers provide sufficient optical transparency to be used in the embodiments of the invention.
The wavelength of operation is related to the pitch Δ of the lattice structure. For a lattice of air holes in silica the band gap is centered at a wavelength given by λ=A for small air filling fraction (ratio of void volume to solid volume) to λ=3.5Λ for large air-filling fraction. As an example, for devices operating in the near infrared (800-2000 nanometers), the lattice pitch can be designed in the range from Λ=800-7000 nanometers. The core 5 would typically have a dimension D between D=0.7Λ and 50Λ and the slot 13 would have a minimum width greater than 0.5Λ. The structure would include multiple rows of holes spaced with pitch A and would have an exterior jacket 9 to provide strength. The total diameter of the final fiber or waveguide would be between 50 microns and 500 microns.
In the fiber sensor 3 illustrated in FIG. 2A , the slot 13 is a single-sided slot having parallel, opposing side walls. Preferably, the slot 13 extends the length of the fiber sensor 3 in order to maximize exposure of the hollow core 5 to the ambient atmosphere. Slot 13 is radially oriented with respect to the circular cross-section of the fiber sensor 3. Such a single-sided slot 13 would have the advantage of relatively low losses for a beam of laser light transmitted through the hollow core 5 having a wavelength within the “forbidden zone” of the cladding 7, while the radial orientation of the slot 13 minimizes fluid flow resistance of outside gasses or liquids into the hollow core 5. Any losses could be further reduced by coiling the fiber sensor such that the slot 13 faced the inner diameter of the resulting coil or spiral for all the reasons given with respect to the FIG. 10 embodiment of the invention discussed hereinafter. In the fiber sensor 25 illustrated in FIG. 2B , a single-side slot 26 is also used. However, slot 26 is offset from the center of the hollow core 5 in a semichordal orientation that intersects with the bottom of the hollow core 5 as shown in order to minimize losses that may result from an overlap between “core” and “slot” modes of conducted light.
In the fiber sensors 27 and 29 illustrated in FIGS. 2C and 2D , double-sided diametral slots 28 a, b and 30 a, b are used. Such double sided slots 28 a, b and 30 a, b have the advantage of reduced fluid flow resistance as compared to the single- sided slots 11 and 26 discussed with respect to FIGS. 2A and 2B , which in turn increases sensitivity and reduces response time. However, these advantages are accompanied by somewhat larger losses in the light conducted through the fiber sensors 27 and 29. Also, the double-sided slots 28 a, b and 30 a, b cannot extend the full length of the fiber sensor 3, as it is necessary to periodically discontinue the slots so that the two halves of the fiber sensors 27 and 29 stay connected to one another via periodic webs of jacket 9. The center orientation of the diametral slot 28 a, b of the fiber sensor 27 maximizes fluid flow through the hollow core 5, while the offset orientation of the chordal slot 30 a, 30 b of the fiber sensor 29 provides the same advantages in reducing overlapping modes as was discussed with the fiber sensor 25 of FIG. 2B with some reduction in fluid flow.
The fiber sensors 32 and 36 illustrated in FIGS. 2E and 2F have the same slot orientations as described with respect to FIGS. 2B and 2D , but with wider slots 34 and 37 a, b, respectively, in order to improve fluid flow, but at a likely price of increased attenuation in optical signals transmitted therethrough.
Minimum mechanical bend radius—the threshold bend radius for which the bend-induced stresses will lead to failure in a time shorter than the acceptable lifetime of the fiber in a given application. When a fiber is bent, the outside of the bend is under tensile stress and the inside under compressive stress. The bending stress can be calculated as:
σbending=E(r f/ R)
where: E=Young's modulus=10440 kpsi (72 GPa)
σbending=E(r f/ R)
where: E=Young's modulus=10440 kpsi (72 GPa)
rf=Fiber radius
R=Bend radius
Under such stress, the time to failure can then be approximately calculated using a simple power law model:
T f=(σp/σa)m
where: Tf=Time to failure (seconds)
T f=(σp/σa)m
where: Tf=Time to failure (seconds)
σp=Prooftest stress
σa=Application stress=bending stress or σ bending
m=Fatigue factor (typically 20 for standard fibers)
In the fibers embodied in this application we anticipate that m will be significantly reduced because of the complex surface geometry. One way to improve the time to failure is to reduce the fiber radius rf thereby reducing the bending stress.
The structure 160 used in FIGS. 11A-11C is an example of a multimode core 162. For some applications (including interferometric detection) it may be advantageous to have single-mode propagation in the hollow core of the ridge waveguide. However, in order to achieve fast response times and high sensitivity it may be advantageous to have a large core (as shown in FIG. 11A ) that supports many optical modes.
Finally, FIGS. 13A-13F illustrates different guided modes of a same embodiment of the invention. FIGS. 13A and 13B illustrate modes that are guided in the core only, while FIGS. 13C and 13D illustrate modes that are guided in both the core and the slab. FIGS. 13E and 13F illustrate modes that are guided exclusively in the slab.
In addition to the optical modes shown in FIGS. 13A-13F there are additional optical modes that exist along the inner surface boundaries of the structure. These additional modes are referred to as surface modes and they only exist when the appropriate surface termination is chosen. In FIG. 13A it can be seen that the core can be formed by cutting a perfect circle of material out of the periodic lattice. Because of the existing air holes that define the structure, this removal of material leaves behind a fluted shape. Likewise the slab can be formed by cutting a rectangular slot out of the periodic lattice leaving behind a fluted air channel. The relative positions of the aforementioned circle and rectangle with respect to the lattice periodicity define the surface terminations in the core and slab regions. The surface termination may be different in these regions so that surface modes may only exist in part of the ridge waveguide. The surface modes have an enhanced interaction with the surface of the structure and thus it may be advantageous to coat the ridge waveguide surface with material to detect the presence of target species through chemical binding, for example.
The embodiments in FIGS. 1-13 can be fabricated using a fiber-draw processes, extrusion processes, direct machining (such as drilling or milling) or planar-processing techniques as found in semiconductor device fabrication. The design of the sensor 3 may be modified to accommodate the processing requirements while maintaining the advantages of the invention. In planar geometries the device may be fabricated at the final intended scale. In fiber geometries the structure can be fabricated in a macroscopic preform that can be reduced in size to attain the desired scale to achieve the properties required for the invention.
While this invention has been described with respect to a number of specific examples, many variations, modifications and additions to this invention will become apparent to persons of skill in the art. All such variations, modifications and additions are intended to be encompassed within the invention, which is limited only by the appended claims and equivalents thereto.
Claims (18)
1. An optical waveguide comprising:
(i) a hollow core portion that defines a light transmission path through said waveguide;
(ii) a cladding at least partially surrounding a hollow core portion, such that said core portion extends along or parallel to a longitudinal, center axis of said cladding, and
(iii) at least one elongated side opening in said cladding that extends parallel to said longitudinal center axis and exposes said hollow core portion to the ambient environment, wherein the hollow core portion and elongated opening jointly support at least one bound optical mode, such that said hollow core portion, said elongated opening, and said cladding form an optical ridge waveguide; and
(iv) a coating situated on a surface of at least a portion of said ridge waveguide.
2. An optical waveguide comprising:
(i) a hollow core portion that defines a light transmission path through said waveguide;
(ii) a cladding at least partially surrounding a hollow core portion, such that said core portion extends along or parallel to a longitudinal, center axis of said cladding, and
(iii) at least one elongated side opening in said cladding that extends parallel to said longitudinal center axis and exposes said hollow core portion to the ambient environment, wherein the hollow core portion and elongated opening jointly support at least one bound optical mode, such that said hollow core portion, said elongated opening, and said cladding form an optical ridge waveguide; and a liquid is contained within the hollow core portion and the elongated opening.
3. The optical waveguide defined in claim 2 , wherein said cladding includes a photonic band gap structure that partially surrounds said hollow core portion.
4. The optical waveguide defined in claim 2 , wherein said cladding includes a microstructured material having a periodic variation in an index of refraction.
5. The optical waveguide defined in claim 2 , wherein said cladding includes a Bragg reflector including alternating layers of material having different indexes of refraction that partially surrounds said hollow core portion.
6. The optical waveguide defined in claim 2 , wherein said cladding includes a plurality of hollow core portions which are optically coupled to one another and wherein said elongated opening in said cladding exposes at least one of said hollow core portions to the ambient environment.
7. The optical waveguide defined in claim 6 , wherein said cladding includes a plurality of elongated openings, each of which penetrates said cladding in a direction transverse to said longitudinal axis and exposes a different one of said hollow core portions to the ambient environment.
8. An optical waveguide comprising:
(i) a hollow core portion that defines a light transmission path through said waveguide;
(ii) an acrylate cladding at least partially surrounding a hollow core portion, such that said core portion extends along or parallel to a longitudinal, center axis of said cladding, and
(iii) at least one elongated side opening in said cladding that extends parallel to said longitudinal center axis and exposes said hollow core portion to the ambient environment,
wherein the hollow core portion and elongated opening jointly support at least one bound optical mode, such that said hollow core portion, said elongated opening, and said cladding form an optical ridge waveguide.
9. The optical waveguide according to claim 8 wherein said acylate is a polymer.
10. The optical waveguide according to claim 8 wherein said acylate is perfluorinated polymer.
11. The optical waveguide according to claim 8 wherein said acylate is PMMA.
12. The optical waveguide defined in claim 8 , wherein said cladding includes a photonic band gap structure that partially surrounds said hollow core portion.
13. The optical waveguide defined in claim 8 , wherein said cladding includes a microstructured material having a periodic variation in an index of refraction.
14. The optical waveguide defined in claim 8 , wherein said cladding includes a Bragg reflector including alternating layers of material having different indexes of refraction that partially surrounds said hollow core portion.
15. The optical waveguide defined in claim 1 , wherein said cladding includes a photonic band gap structure that partially surrounds said hollow core portion.
16. The optical waveguide defined in claim 1 , wherein said cladding includes a microstructured material having a periodic variation in an index of refraction.
17. The optical waveguide defined in claim 1 , wherein said cladding includes a Bragg reflector including alternating layers of material having different indexes of refraction that partially surrounds said hollow core portion.
18. A method of making an optical waveguide, comprising:
(i) making a microscopic perform comprising: a cladding at least partially surrounding a hollow core portion that extends along or parallel to a longitudinal, center axis of said cladding, and at least one elongated side opening in said cladding that extends parallel to said longitudinal center axis and exposes said hollow core portion to the ambient environment; and
(ii) reducing said microscopic perform in size thus providing a optical waveguide comprising:
a cladding at least partially surrounding a hollow core portion that extends along or parallel to a longitudinal, center axis of said cladding and defines a light transmission path through said waveguide, and at least one elongated side opening in said cladding that extends parallel to said longitudinal center axis and exposes said hollow core portion to the ambient environment,
wherein the hollow core portion and elongated opening jointly support at least one bound optical mode.
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US12/008,750 Expired - Fee Related US7428360B2 (en) | 2007-02-27 | 2008-01-14 | Optical waveguide sensor and method of manufacture |
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EP (1) | EP2115428A2 (en) |
JP (1) | JP2010519557A (en) |
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US20140037261A1 (en) * | 2012-08-01 | 2014-02-06 | Gwangju Institute Of Science And Technology | Optical fiber for chemical sensor |
US9958603B2 (en) * | 2012-08-01 | 2018-05-01 | Gwangju Institute Of Science And Technology | Optical fiber for chemical sensor |
US20170097464A1 (en) * | 2015-10-06 | 2017-04-06 | General Electric Company | Microstructured optical fibers for gas sensing systems |
US9791619B2 (en) * | 2015-10-06 | 2017-10-17 | General Electric Company | Microstructured optical fibers for gas sensing systems |
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US7343074B1 (en) | 2008-03-11 |
WO2008106011A2 (en) | 2008-09-04 |
JP2010519557A (en) | 2010-06-03 |
US20080205837A1 (en) | 2008-08-28 |
CN101617210A (en) | 2009-12-30 |
WO2008106011A3 (en) | 2008-10-16 |
TW200900769A (en) | 2009-01-01 |
TWI386695B (en) | 2013-02-21 |
EP2115428A2 (en) | 2009-11-11 |
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